This invention relates to an active filter and, more particularly, to an electronic active filter with improved filter characteristics.
An ideal filter would have a frequency response or transfer characteristic such that it should provide a high Q, that is, a sharp attenuation outside of a selected bandpass portion, and be stable, that is, free of thermal drift and noise interference.
Conventional active filters are, however, susceptible to thermal drift, phase delays and noise, as it is generally known. Various techniques have been devised to overcome these problems with some degree of success. Among the solutions that have been used are feedback techniques or some type of schemes designed to introduce phase lead that would cancel the phase lag associated with the parasitic elements of the filter. None, however, has been found fully satisfactory.
The object of the present invention is to provide an active filter which eliminates substantially parasitic effects of active elements of the filter.
It is another object of the present invention to provide an active filter which is not susceptible to thermal drift and which provides substantially enhanced filter characteristics.
It is yet another object of the present invention to provide an active filter which is simpler in structure compared to the conventional active filter.